Biological complexity: zebrafish smell ATP for food (Introduction)

by David Turell , Friday, September 01, 2017, 16:54 (2640 days ago) @ David Turell

They are shown to smell molecules from organisms they eat:

http://www.the-scientist.com/?articles.view/articleNo/50151/title/Fish-Smell-ATP-to-Fin...

"Studies have shown that fish sense ATP, the cellular unit of energy, and follow concentration gradients of the molecule released by zooplankton to track down their next meal. Testing zebrafish in the lab, neurobiologist Yoshihiro Yoshihara of the RIKEN Brain Science Institute in Japan and colleagues found that ATP appeared to activate a small number of short, pear-shape olfactory sensory neurons at the very tip of the nose.

"When the researchers hunted for ATP receptors in the zebrafish genome, they found a novel receptor called A2c. Cell culture experiments revealed that A2c was not directly activated by ATP, however; two enzymes, tissue-nonspecific alkaline phosphatase (TNAP) and CD73, first broke down ATP to adenosine, which then bound the receptor and triggered the neurons in the nose to fire. Signals from these neurons then activated a single large cluster of nerve endings, or a glomerulus called IG2, in the olfactory bulb of the zebrafish brain.

"A database search of available genomes showed that the A2c receptor is found in fish and amphibian species, but not in terrestrial reptiles, birds, and mammals. “The A2c receptor must serve a very fundamental function in all the aquatic lower vertebrates,” Yoshihara says."

Comment: Even in fairly primitive animals the biologic systems they use are highly complex, as this study shows. To be developed in evolution two large very specific enzymes must be found (or invented) to have it all work. We do not know how this happens, but it did. Design?